448 Copperas . 
form and prevent the too drying effect of the sun, the peat 
is l^id in heaps, only three or four inches in thickness under 
sheds thatched with straw, where they remain for a few 
days, after which they are ready for lixivation, This is 
done by throwing the peat into large vats of masonry and 
covering it with rain water, which flows through the heaps 
and is collected for the purpose, and also with some of 
the mother v, ater of the former crystallization. It is then 
evaporated and crystallized in the method already describ- 
ed. 
In some places the pyrites requires roasting before it 
can be decomposed by the action of the air. Thus at 
Geyerin Saxony, the pyrites, after being exposed for some 
time to the air, is soaked in water for twelve hours, then 
roasted as in the ordinary method of roasting ores, in a 
large bed upon faggots, on which about seventy or eighty 
quintals at a time are heated red-hot, and in this state 
plunged again into water. This is repeated six times 
successively with the same pyrites, by which the water 
becomes strongly impregnated with vitriol and is after- 
wards evaporated and crystallized as usual. 
A quantity of heat is always generated during the pro- 
cess of vitriolization, both in the first combination of iron 
with sulphur and the subsequent oxygenation of the sul- 
phur, and consequent conversion into sulphuric acid, 
which enables it to dissolve the iron and form the sulphat 
required. 
The degree of the heat produced, and the quantity of 
moisture which the pyrites receives (by rain or other sour- 
ces) are the circumstances that principally regulate the 
production of vitriol, both as to quantity and time of its 
production. Too much heat actually kindles the mass f 
the remaining sulphur takes fire, and an immense quanti- 
ty of sulphureous acid vapour is given off to a great dis- 
tance around.. Where this takes place, little or no vitriol* 
